In 1997, about 9.4 percent of all girls ages 15 to 19 became pregnant a total of 872,000 pregnancies, the Centers for Disease Control and Prevention reported Tuesday. Fifty-five percent gave birth, 29 percent had abortions and the rest miscarried.

The teen pregnancy rate fell by 4.4 percent between 1996 and 1997, the most recent year for which data is available, continuing a trend that has marched through the 1990s.

Pregnancy rates are significantly higher in low-income communities, and black and Hispanic girls are more than twice as likely to get pregnant as white girls are. Still, the rates are falling among all races.

Most of the teen pregnancies are among 18- and 19-year-olds, though some 6.4 percent of girls ages 15 to 17 were pregnant in 1997. That's down 21 percent since the peak in 1990.

Overall, the teen pregnancy rate fell 19 percent in 1997 from its peak in 1991, and was the lowest since 1976, when the government began keeping records. The abortion rate fell by nearly a third since 1990, also reaching a record low.

The teen pregnancy rate is derived by combining the number of teens who give birth with estimates for abortion and miscarriage rates. Because data on abortion are difficult to collect, the statistics are several years old by the time they are released.

Teen-agers particularly those who are young and unmarried are rarely equipped emotionally or financially for parenthood, and there's near universal agreement that reducing their pregnancy rates is among the most positive social trends of the 1990s.

Federal surveys show that during the 1990s, teens were more likely to use birth control and less likely to have sex. In 1995, 51 percent of teen girls said they'd had sex, down from 55 percent in 1990; among boys, it dropped from 60 to 55 percent between 1988 and 1995. And the sharp drop in the abortion rate suggests that most of the pregnancies being avoided were unwanted.

But it's much harder to figure out why teens decide against having sex or for using birth control in the first place. "That is almost wholly up to speculation," said researcher David Landry of the Alan Guttmacher Institute, which focuses on reproductive health issues and collects some of the abortion data used in the government report.

Those who support a greater emphasis on abstinence telling teens to just say no to sex tend to credit an increase in support for these programs, which saw a massive infusion of government money beginning in 1997.

Those who believe the availability of birth control is key point to new, more reliable methods of contraception. That includes Depo-Provera, an injectable drug that came onto the market in 1993, and Norplant, capsules that are surgically inserted under the skin and last about five years.